Method of making mirrors



Sept. 10, 1940. w. PEACOCK 2,214,475

METHOD OF MAKING MIRRORS Filed Oct. 18, 1938 I i v I l 10 A; 6 i i l t l I l'lidenfior WKLUAM PEAcocM,

Patented Sept. 10, 1940 UNITED STATES METHOD OF MAKING MIRRORS William Peacock, Philadelphia, Pa... assignor, by meme assignments, to Peacock Laboratories,

Inc., Toledo, Ohio, a

corporation of Ohio Application October 18, 1938, Serial No. 235,661

8Claima.

This invention relates to an improved method of applying a surface coating or layer of metallic silver which may serve as a reflecting medium when applied to transparent bodies, such as glass,

6 or as a surface decorative medium when applied to translucent or opaque bodies, this application being a continuation in part of my copending application, Serial No. 210,315, filed May 2'7, 1938.

Heretofore and prior to this invention it has 10 been the common practice in the making of mirrors to apply a silvering solution to one surface of a glass while maintaining said surface in a perfectly horizontal plane, the metallic silver being permitted to deposit out of the solution and 1| upon the glass surface. While various expedients have been resorted to in order to insure maintenance of the glass surface in properly leveled condition, this leveling operation nevertheless entails considerable difliculties and the expenditure of much valuable time. Also, in order to' insure uniform spreading of the solution over the leveled surface of the glass, such surface must be maintained constantly wetted with the result that the water so present upon the glass surface often ini terferes with the proper uniform deposition of the silver out of the silvering solution.

In addition, improper leveling of the surface to be silvered results not only in considerable variations in the thickness of the deposited metallic ".silver film in diflerent areas thereof, the silver film being quite heavyor dense over one area and considerably lighter or thin over another area of the silvered surface, but also in inadequately coated edges.

88 Moreover, in the conventional methods of silvering mirrors wherein the silvering solution is necessarily poured over the surface to be silvered, it is an exceedingly difilcult task to prevent or detect the deposit of non-reflecting decomposiw tion products of the silvering solution'along with the reflecting metallic silver. Should these decomposition products be removed during the final rinsing and drying operation, objectionable pinholes are produced, while should such products 5 perchance remain bound in the silver film, they nevertheless result in translucent spots clearly visible to the eye when the finished mirror is held up to the light.

The present invention has as its object the 50 elimination of the aforementioned objections to and difilculties encountered in the old method of silvering mirrors by the use of separately atomized silver and reducing solutions which may be sprayed onto the glass or other surface while the 55 latter is maintained in a plane inclined at a sub- (01. ill-69.1)

stantial angle with respect to the horizontal and which react with sufficient rapidity and degree to insure the deposit of a silver film of a density and homogeneity adequate for mirror purposes.

A further and important object of the present invention is to provide silvering solutions of such formulae that they are suitable for use in atomized state without danger of creating explosive mixtures, it being well known that when accelerating agents, such as sodium or potassium hydroxide are mixed with the usual silver ammonio nitrate solution to form a single mixture a dangerously explosive combination is obtained. To minimize this danger it has been the practice to introduce the caustic alkali at as late a time as possible, the resultant mixture being used without further delay because the explosiveness of the mixture increased with its age. Obviously, this resulted in considerable waste of solutions because unless all of the mixture were employed within a relatively short interval after its preparation, in the interest of safety the unused prepared solutions were required to be destroyed. In addition, I have found that in order to obtain most satisfactory results by the use of the spray method above set forth, certain compounds, such as hydrazine sulphate, hydrazine hydrate and hydrazine nitrate, serve most effectively as silver reducing agents, and it is among the objects 'of this invention to provide a method whereby such compounds may be safely employed in conjunction with a caustic soda accelerator in the production of silvered mirrors by the spray method aforesaid.

Other objects and advantages of the invention, such as those relating to economies effected by the use of the hereinafter disclosedmethod and to the improved character of the silver film or coating so obtained, will be apparent more fully hereinafter.

In the accompanying drawing which illustrates more or less schematically the method of practicing the present invention, Figure 2 illustrates a convenient scheme for supporting a mir ror to be silvered in the desired inclined position, while Figure 1 illustrates schematically a. solution spraying apparatus for performing the spraying operation.

Referring now more particularly to these figures, it will be observed that the spraying apparatus essentially includes two solution tanks l0. and II respectively adapted'to contain sprayable solutions A and B which, when mixed together, act to deposit metallic silver upon the surface to be coated. In each instance the silver solution contains silver nitrate as the principal ingredient, while the reducing agent consists of a hydrazine compound, such as hydrazine sulphate, hydrazine nitrate or hydrazine hydrate. While the composition of these solutions may vary, of course, it is preferred that they be produced in accordance with the following exemplary formulae.

Where hydrazine sulphate, nitrate or hydrate is employed in the formulation of the reducing solution, any of the following formulae may be used, it being understood, of course, that in all of the following examples solutions Al and 3!, A2 and B2, etc., are employed cojointly:

Example 1 Solution Al Solution Bl This is preferably a solution oi Solution consisting oi 2 oz. of silver ammonio nitrate which hydrazine sulphate (or nitrate is prepared by dissolving 1 oz. or hydrate) dissolved in 100 oz. of silver nitrate in 100 oz. oi oi water. distilled water to provide an initial solution into which is added and stirred 1% oz. oi ammonium hydroxide.

iixample 2 Solution A2 Solution B2 Sameassolution Al above Same as solution B1 above to which is added ,5 oz. of sodium hydroxide.

Emample 3 Solution A3 Solution B3 Silver nitrate (1 oz.) dissolved in Solution consisting oi h drazine 100 oz. of water. sulphate (or nitrate or ydrate) (2 oz.) and ammonium hy' droxide (1% oz.) dissolved in 100 oz. of water.

Example 4 Solution A4 Solution B4 Someassolntion A3 above Same as solution 33 above to which is added oz. of sodium hydroxide.

Example 5 Solution B5 Solution A5 Solution consisting oi 1% oz. of ammonium hydroxide dissolved in 100 oz. of water.

Solution consisting oi 1 oz. oi

silver nitrate and 2 oz. of hydrazine sul hate (or hydrate which is added }6 oz. of sodium hydroxide.

It is to be understood that in the above formulae for the several solutions A! and BI, A2 and B2, A3 and B3, etc., the proportions stated are not intended to be critical, are approximate and may be varied within reasonable limits. For example, I have found that by increasing materialiy'the proportion of ammonium hydroxide employed, the speed of reaction between the silver ammonio nitrate and the reducing agent may be so decreased that an extremely thin or transparent iihn of silver may be obtained, a result which would have been practically impossible were it not for the control obtained by reducing the speed of reaction. Similarly, other results and effects may be' obtained by varying within rather wide limits the proportions of the other ingredients employed. Experience has demonstrated, however, that the above stated proportions produce very desirable results for general purposes.

It is to be observed that in no instance do any of the formulae provide for the mixing together in a single preparedsolution silver nitrate and the caustic alkali accelerator, sodium hydroxide. Instead, the solutions respectively containing the silver nitrate and the caustic alkali are always mutually exclusive. In addition, it will be noted that in none of the above formulae is there provided a. single prepared solution which commonly contains the silver nitrate, the ammonium hydroxide and the reducing agent. This caus.ic alkali is employed for the purpose of accelerating the chemical reaction between the silver ammonio nitrate solution and its reducing solution, but where the latter is sufliciently active per se to rapidly effect the deposition of the metallic silver out of the silver solution by reduction of the latter, as in Examples 1, 3 and 5, or where it may be desired to reduce the speed of reaction, the caustic may be dispensed with. In the case of Examples 2, 4 and 6, although the reduction is effected quite rapidly by the hydrazine compound, the caustic alkali is nevertheless employed to still further speed up the reduction, as where the circumstances may require it. In all cases,'the caustic alkali may be the sodium hydroxide aforesaid or its equivalent, potassium hydroxide.

in the use of the solutions A and B as above prepared, approximately equal quantities of each are respectively maintained in the containers in and ii in order to insure against the accidental or unintentional exhausting of one solution supply without at the same time exhausting the other, thereby obviating the possibility of spraying only one solution upon the surface to be silvered. Also, where the containers i0 and H are supported in elevated position so as to provide a gravity feed for the solutions to the spray gun by maintaining equal solutions in the containers to and ii the maintenance of equal head pressures is insured, thus providing for equalized delivery of'the separated solutions to the spray gun.

The spray gun I2 is connected by the conduit l3 to a suitable source of compressed air supply, the compressed air being delivered from the gun by way of its discharge nozzle H, the gun being When compressed air is admitted to the spray gun by opening the control valve for the latter, such air passes through and is discharged from the nozzle H with suitable velocity. As the compressed air passes the inner open ends of the fittings and II the solutions A and B are sucked or drawn out of the tanks 00 and I l by way of the flexible conduits l6 and l I and into the air stream where they are atomized and intimately mixed together. While this atomization and intimate mixture of the solutions A and B occurs instantly at the discharge end of the nozzle H, the resultant reaction of said solutions is not completed before the atomized, mixture is brought into contact with the surface to be covered by the metallic silver which is the product of such reaction.

Preferably, the flexible conduits l6 and I! are each provided with suitable valves 22 and 23 conveniently located within reach of the operator of the spray gun, these valves being opened subsequently to the opening of the compressed air control valve in the spray gun. With .the valves 22 ahd 23 closed, the supply of the solutions A and B is, of course, interrupted so that only so much of these solutions may be used as is necessary to complete a given silvering operation.

The flexible conduits or tubes l8 and I1 permit independent movement of the spray gun so that it may be readily moved about to direct the discharge therefrom against the proper surface without disturbing the position of the containers l0 and l I. In the use of this easily directed spray gun for mirror silvering purposes, the plate glass to be silvered is supported in a position such as is shown in Figure 1. As is therein illustrated, the plate glass 24 is mounted flatwise upon the inclined surface of an easel-like frame 25 which may be suitably supported in any manner upon a table 28. Preferably, the easel 25 is so arranged that its angle of inclination with respect to the horizontal may be varied within wide limits, since it may be desirable in some instances to support the mirror plate 24 in a vertical plane and in other instances in a plane forming an acute angle with the horizontal. 7

By spraying the silvering material upon the iii-- clined surface of the mirror plate 24, a silver film is obtained of very high quality. Not only is this film of uniformly even thickness throughout but it is more homogeneous due to the substantial absence of pin-holes. Moreover, should any water be present upon the glass surface as would normally tend to interfere with proper deposition of the metallic silver thereupon, it is washed down and thoroughly removed by the force of the spray,

directed against the inclined surface of the glass. A further and important advantage of the present method resides in the fact that the solutions A and B may be employed at ordinary'room temperatures, in contradistinction to the older methods which usually require heat in the application of the silvering solution. v

The present method is particularly adapted for coating with silver other transparent materials such as are obtained from synthetic resins, cellulosederivatives and the like and which ordinarily so deleteriously aifect and impair the reaction of the usual silvering solutions applied in the customary manner as to produce unsatisfactory mirrors. Accordingly, it will be understood that the present invention is not limited in its application solely to the silvering of glass for mirror purposes, but instead may be generally employed for providing any surface with a reflective or decochemical reaction between said solutions.

2. A method of depositing a film of metallic silver upon the surface of a body which comprises preparing and maintaining in separated relation separate solutions of silver ammonio nitrate and a reducing agent therefor, in simultaneously introducing approximately equal quantities of said solution into a Jet of compressed air, said solutions being entrained in said jet in the immediate vicinity of its discharge into atmosphere whereby said solutions are atomized and intimately mixed together for reaction to produce metallic silver which is adapted to be applied in the form of a homogeneous film over the surfaceto be covered, said reducing solution containing an-agent selected from the group consisting of hydrazine sulphate, hydrazine nitrate, and hydrazine hydrate and an accelerating caustic alkali.

3. A method of depositing a film of metallic silver upon the surface of a body which comprises preparing and maintaining in separated relation separate solutions of silver ammonio nitrate and a reducing agent therefor, in simultaneously introducing approximately equal quantities of said solution into a jet of compressed air, said solutions being entrained in said jet in the immediate vicinity of its discharge into atmosphere whereby said solutions are atomized and intimately mixed together for reaction to produce metallic silver which is adapted to be applied in the form of a homogeneous film over the surface to be covered, said reducing solution containing a hydrazine compound selected from the group consisting of hydrazine sulphate, hydrazine nitrate, and hydrazine hydrate.

4. A method of forming a metallic silver reflecting film upon a glass or like surface which comprises directing against said surface a. compressed air spray in which are atomized and intimately mixed separately formed solutions adapted to react with one another to produce metallic silver, said solutions containing silver nitrate, ammonium hydroxide and a hydrazine compound selected; from the group consisting of hydrazine sulphate, hydrazine nitrate, and hydrazine hydrate, at least one of said last-named ingredients being included in a solution separate from that containing the other of said ingredients.

5. A method of forming a metallic silver reflecting film upon a glass or like surface which comprises directing against said surface a compressed air spray in which are atomized and intimately mixed separately formed solutions adapted to react with one another to produce metallic silver, said solutions containing silver nitrate, ammonium hydroxide, a reducing agent selected from the group consisting of hydrazine sulphate, hydrazine nitrate and hydrazine hydrate, and an accelerating caustic alkali, at least one of said first three named ingredients being included in a solution separate from that containing the other two of said first three named ingredients, and said caustic alkali being included in the solution other than that containing'the silver nitrate.

6. A method of forming a metallic silver refiecting film upon a glass or like surface which comprises directing against said surface a compressed air spray in which are atomized and intimately mixed at least two separately formed solutions adapted to mutually react to produce metallic sllverfsaid solutions containing silver nitrate, ammonium hydroxide, a reducing agent selected from the group consisting of hydrazine sulphate, hydrazine nitrate and hydrazine hydrate and a caustic alkali accelerator and being characterized in that no one of said solutions contains all of the three first named ingredients and further in that the solutions respectively containing the silver nitrate and caustic alkali are mutually exclusive.

7. A method of forming a film of metallic silver upon the surface of a body which comprises mixing in air a liquid spray containing silver ammonio nitrate and a liquid spray containing a reducing agent for said silver ammonia nitrate, and directing said mixed spray against the surface of the body to be covered, the reducing agent being selected from the group consisting of hydrazine sulphate, hydrazine nitrate, and hydrazine hydrate, said metallic silver deposit having a high coeiiicient of reflection at both the back and front surfaces thereof,

8. A method of forming a film of metallic silver upon the surface of a body which comprises positioning the body so that its surface to be coated is inclined to the horizontal, preparing separate solutions one of which contains silver ammonio nitrate and the other of which contains a reducing agent therefor selected from the group consisting of hydrazine sulphate, hydrazine nitrate, and hydrazine hydrate, mixing in proximity to the surface to be coated a liquid spray of the solution containing silver ammonio nitrate and a liquid spray of the solution containing the reducing agent, and directing said mixed spray against the inclined surface so that the reaction product of said silver ammonio nitrate and reducing agent forms an adherent homogeneous metallic silver deposit thereon having a high coeflicient of reflection at both the back and front surfaces thereof, the mixed spray having sufllcient force to eflect a washing down of the inclined surface being coated.

WILLIAM PEACOCK. 

